Get fast Cycles render like in the viewport?

Artistic Support Materials and Textures
1

Hi folks,

I’ve only been messing around with Cycles for a couple of days (was only using Eevee previously), and one fundamental thing is really puzzling me:

I’ve got a really simple scene (for test purposes) that consists of a highly reflective sphere and an off-screen image that’s reflecting in the sphere. The animation part of the scene is the rotation of the off-screen image.

Now, when i jump my playhead in the scene from one frame to another, the image will update or “render” in the viewport in around a second. Ok, maybe the quality isn’t going to have Pixar quaking in their boots, but for my purposes it’s good enough, and if i could get that quality of render (that i see within one second) over into my compositor, i’d be more then happy.

However, when i perform a render of my 50 frames, each frame is taking around 30 seconds to render!

I tried putting my render samples setting very low, like 10, and then i get pretty quick renders, but it seems to me that the render i get in the viewport within a second is much higher quality!

Could anyone shed any light on this or give me some tips on speeding up the render times?

Thanks!

2

There’s a lot of potential reasons, but the most likely is that you have modifiers that have higher levels for render, than viewport. The most common would be subsurf which by default is 1 for viewport 2 for renders, which will cause slower full render than viewport renders.

3

Ah, ok, i’ll look into that, thanks!

4

Bonestudio is working at viewport denoising. Right now the build does not have it but they say fairly soon. keep an eye open on the Graphicall site. https://blender.community/c/graphicall/kdbbbc/

5

also depends on the quality of render you want or need
the higher the quality the longer the render will be that is normal

viewport is only limited to the screen size around 1 K and not taking into account most of the lighting so it will always be faster
which is normal

to get faster render then use the EEVEE

happy bl

6

There is a fair bit of time in file writing as well. The viewport renderer just dumps an image to the screen, pressing f12 has to save out that file, and depending on the resolution and settings, that can take a fair bit of time.

If you pull up the system console when rendering, it will show you the time spent rendering and the time spent saving:
image

Depending on your output file settings it can take a good bit of time to compress the file as well. Those .25 second saving times were with .png compression set to 15%, increasing compression to 100% increasess that saving time to almost 5 seconds, a 20x increase in time taken saving.

7

Thanks!

That PNG compression is losseless, like a zip file, right?

If you’re not worried about disk space, is there any benefit to compressing?

Won’t my compositor also work faster with no compression used?

8

I believe it is lossless, but I’m sure about how it will affect compositing speed.
Run a few test renders to see how it effects render time on your system.